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The Porsche Taycan's Two-Speed Gearbox

wired.com

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Re: The Porsche Taycan's Two-Speed Gearbox

#11

Post by ferongr »

efraim wrote: post #10
mywittyname wrote: post #2

I'm surprised ZF/Porsche didn't turn this into an eCVT, as an eCVT (a la Prius) has probably the same complexity, but with the added benefit of having more ratios. I suspect it would also reduce shock loads on the transmission as a result of shifting. I wish the article would have gone into this, because I suspect Porsche said no more for marketing reasons rather than technical ones, as CVTs are universally hated in…

A CVT can't handle as much torque as a gear-based transmission.

The e-CVT has nothing to do with actual CVTs, it's a planetary "torque split" gearbox that's very robust.

Re: The Porsche Taycan's Two-Speed Gearbox

#12

Post by rconti »

aidenn0 wrote: post #4

FWIW the original Tesla roadster was also a 2 speed, but they dropped the gearing as soon as they could meet their original top-speed without it.

Yeah, and it was apparently prone to breaking (I learned this from Googling just now). I was pretty sure I drove a 2-speed Roadster back in the day, but wanted to confirm that actually made it to production -- it did. (The Roadsters I drove were Tesla-owned but I'm pretty sure they were full production models).

The more things change, the more they stay the same. I remember Tesla being laughed at for this whole overpriced roadster thing, then because their transmissions were breaking, then because the 'fix' was to produce a "crippled" 1-speed car because they couldn't figure out how to make a transmission that didn't break.

And now, 10 years later, I own a 1-speed one, and, miraculously, the whole thing works on a real sedan, not just a kit car.

Re: The Porsche Taycan's Two-Speed Gearbox

#13

Post by rconti »

jameskilton wrote: post #9
elihu wrote: post #6

Seems logical. I think most manufacturers have just decided that they'd rather use an over-sized motor than deal with a transmission, but if you're willing to tolerate a more complicated drive-train you get more usable power with less weight. Using a transmission might get weird if you have multiple motors, though. For instance, it would be odd to have the front wheels in one gear and the rear wheels in a different g…

From what I've read, the AWD versions of the Model 3 (possibly others) actually do this (different ratios in the front and back). As the article says, Tesla had a hard time building a transmission that wouldn't tear itself apart under the torque of the electric motors. So, they put the front and back motors at different ratios. The back motor is used at lower speeds, and the front motor kicks in at higher speeds.

I'm not sure about the higher speeds vs lower speeds thing. Anyway, Tesla knows the gear ratios in both units, they can apply power as necessary to get the exact torque split the computer wants.

Re: The Porsche Taycan's Two-Speed Gearbox

#14

Post by Mikeb85 »

gleglegle wrote: post #5

It's a little surprising that even with a two-speed Gearbox the Taycan has neither better range nor low range 0-60 acceleration than the Tesla P100D (which has the same size battery). Obviously spec comparisons aren't the whole story and the handling and high-range acceleration may be better on the Taycan. Looking forward to seeing more comparisons and already glad to see more EV models in this category. Edited incor…

Porsches have never really been about straightline speed. Always about overall performance and a sports-car feeling.

I'm guessing they optimized things like power, gearing and weight placement to offer good acceleration through a range of speeds with amazing handling and decent range at speed.

Re: The Porsche Taycan's Two-Speed Gearbox

#15

Post by madmulligan »

mywittyname wrote: post #2

I'm surprised ZF/Porsche didn't turn this into an eCVT, as an eCVT (a la Prius) has probably the same complexity, but with the added benefit of having more ratios. I suspect it would also reduce shock loads on the transmission as a result of shifting. I wish the article would have gone into this, because I suspect Porsche said no more for marketing reasons rather than technical ones, as CVTs are universally hated in…

The main advantage of the eCVT is the ability to seamlessly combine the power from two motor-generator units and an ICE (as in the Prius) while holding the ICE in the RPM range you want it. Here, there is only one electric motor and keeping it at a certain RPM range (other than below it's max) isn't really important. While a CVT will get you smooth ratio changes, you are still constrained by a minimum and maximum gear ratio, a range which is relatively small compared to this kind of two speed (in this case you can have two gear ratios that are super far apart, as an electric motor makes the same torque regardless of the RPM, unlike an ICE, where you want your gear ratios close to help stay in the powerband). As for CVT's being universally hated in performance circles, they're only universally hated by the same kind of people that hate flappy paddle dual clutch transmissions, i.e people who don't care or know what is actually faster, more reliable, and more efficient in different use cases, but only care about a clutch and an H-pattern shifter.

Re: The Porsche Taycan's Two-Speed Gearbox

#16

Post by rconti »

Mikeb85 wrote: post #14
gleglegle wrote: post #5

It's a little surprising that even with a two-speed Gearbox the Taycan has neither better range nor low range 0-60 acceleration than the Tesla P100D (which has the same size battery). Obviously spec comparisons aren't the whole story and the handling and high-range acceleration may be better on the Taycan. Looking forward to seeing more comparisons and already glad to see more EV models in this category. Edited incor…

Porsches have never really been about straightline speed. Always about overall performance and a sports-car feeling. I'm guessing they optimized things like power, gearing and weight placement to offer good acceleration through a range of speeds with amazing handling and decent range at speed.

True, and the Taycan may well be a better car in many ways. But a discussion of the gearbox has nothing to do with handling or sports car feeling.

I'm wondering what we're missing here. 5% efficiency improvement at high speeds isn't anything to write home about today. The transmission is a known quantity -- it's just gears, it won't get more efficient as they develop it. The efficiency of the whole system (battery/drivetrain/regen/motor/aero/etc) can be optimized quite a bit going forward, but if the 2-speed transmission will only ever get us a 5% increase, I'm not sure it's worth the added weight and complexity.

Obviously Porsche knows what they're doing, and it may be about thermal management on the Autobahn more than about outright efficiency, but I'm skeptical.

If this were 2010 I'd say "yeah, obviously Porsche knows something about building a real sedan that you can take on a real highway trip, Tesla has no idea what they're doing".

But, having produced actual sedans that actually work, and Porsche going with a more complicated system for 5%.. I don't know what I'm missing.

Re: The Porsche Taycan's Two-Speed Gearbox

#18

Post by whalesalad »

mywittyname wrote: post #2

I'm surprised ZF/Porsche didn't turn this into an eCVT, as an eCVT (a la Prius) has probably the same complexity, but with the added benefit of having more ratios. I suspect it would also reduce shock loads on the transmission as a result of shifting. I wish the article would have gone into this, because I suspect Porsche said no more for marketing reasons rather than technical ones, as CVTs are universally hated in…

CVT transmissions can’t handle the power. They’re also universally hated by everyone except people who merely use a car to get from A to B. A Porsche owner is the polar opposite of someone who would tolerate a CVT.

Re: The Porsche Taycan's Two-Speed Gearbox

#19

Post by jason46 »

gleglegle wrote: post #5

It's a little surprising that even with a two-speed Gearbox the Taycan has neither better range nor low range 0-60 acceleration than the Tesla P100D (which has the same size battery). Obviously spec comparisons aren't the whole story and the handling and high-range acceleration may be better on the Taycan. Looking forward to seeing more comparisons and already glad to see more EV models in this category. Edited incor…

I've not done a whole lot of research but Tesla has it figured it out, compare a Tesla in power and range with the BMW i8. Maybe Porsche can make a better showing than their German counterpart.
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